As a vehicle underbody structure, in patent document 1 (JP-A No. 2007-276614), there is described a structure where a substantially U-shaped recessed portion that extends in a vehicle front-rear direction is formed in the center of a lower surface portion of a fuel tank and where the middle section of an exhaust pipe is disposed in the recessed portion.
Incidentally, taking the liquid surface of the fuel inside the fuel tank as a boundary, the portion on the lower side becomes a liquid layer and the portion on the upper side becomes a gas layer, so when a recessed portion is disposed in the lower portion of the fuel tank as described in patent document 1, the fuel quantity that can be contained in the fuel tank decreases by that amount. Additionally, in order to ensure the fuel quantity containable in the fuel tank, this leads to an increase in the size of the fuel tank.